Supply, Demand and Storage

Demand peak = evening Demand trough = night Domestic demand = the most demand, spiking in the morning and evening, and declining at night Industrial demand = the middle. Has the most night usage, but declines before the morning and stays stable during the day Commercial demand = lowest. Stays relatively consistent all day

• short term weather/climate (e.g. temp and rain) fluctuations • seasonal fluctuations • weekday/weekend fluct in industrial/commercial use and schoolchildren • 24hr day/night fluct • short-term behaviour-related fluct: mealtimes, TV ‘pickup’

• base-load power stations generating elec 24hrs a day even though much less electricity is needed during the night because it is uneconomic to turn the power stations on and off • fluct in demand (e.g. after meals/TV breaks, lower industrial demand outside core working hours). The demand demand for electricity may drop more rapidly than power station output can be reduced • if generated electricity is unused, then it is lost through the heat from cables

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• use of intermittent energy resources (e.g. solar, wind, tidal) • bulk delivery of transported energy resources (e.g. oil, coil, biofuels). Includes politics

overall, higher during the day and evening due to increased demand (see card), and lower at night due to decreased demand a) declines at night because no sun b) increase in wind over night plus imports means the need for gas declines overnight, and it is relatively easy to turn off c) increases over night because more wind due to increased temp difference and air pressure fluctuations d) stable because the reaction is constant and is very easy to turn off so can if needed e) generation of wind at night is higher and other rens (not solar), plus is also low at night because the heating is not on

energy management trying to flatten out supply and demand while reducing electricity costs and grid strain by lowering power consumption during periods of highest demand - trying to store the excess energy generated during low demand so it can be used to meet periods of high demand

• pumped storage HEP • chemical energy • rechargeable batteries • compressed gas

• surplus energy is used to pump water uphill, which stores the energy as grav potential energy • the potential energy can be converted to kinetic energy through water flowing to the lower reservoir turning the turbines and generating elec to meet any peaks in demand • so, pumped storage HEP stations can be much more responsive to changes in demand than stations powered by coal, gas or nuclear • they can go from standby to full power in less than 15 secs, so they can meet sudden increases in demand

• stored fossil fuels, biofuels, and hydrogen store chemical energy • batteries and fuel cells can be used to store chemical energy • rechargeable batteries enable the original chemicals to be reformed using electricity so that the batteries can be reused • however, for fuel cells to continue to operate, new fuel and oxidant chemicals must be supplied

• the efficiency of the storage cycle: the percentage of the electricity used during recharging that is available later • the number of charge-discharge cycles that can be carried out • energy density • cost per unity of energy stored • recharging speed • self-discharge during periods of non-use • safety issues: toxicity, fire risk

a) - lead acid - nickel-cadmium (NiCad) - lithium ion (LiIon) - lithium polymer (LiPoly) b) - lithium-air - gold nanowire - graphene - sodium-ion - bio batteries

• surplus energy can be used to drive a pump that compresses air • the compressed air can be released later to power machinery • compressing the air produces a lot of heat, which may also be stored, e.g. in hot oil or molten salt thermal storage • a compressed air system with heat storage can recover over 90% of the original energy e.g. railways (for example of a cliff/slope) - the braking system drives a compressor to compress a gas and store potential energy - this recovered energy can be used to help push the carriage up hill again

• has been used on a small scale since 1870 • current research focuses on large-scale systems which could produce over 200MW of power from compressed air sored in underground caverns, e.g. salt mines

• degradation and decreased storage over time/limited lifespan • high initial cost • safety concerns which lead to fire/explosion if damaged, overcharged or subjected to high temps

• higher (theoretical?) energy density • lighter • smaller • cheaper

by converting electrical energy into chemical potential energy during charging - when surplus electricity (e.g. from solar or wind) is available, it drives ions from the cathode to the anode through an electrolyte - stores the energy until needed, at which point the process reverses to release electricity

• a larger quantity of fuel can be accumulated for more economic transportation • energy production rates can be kept constant for the most economic use of equipment and workers e.g. coalmines, oil and gas wells • any surplus energy from intermittent supplies can be stored until it is required (e.g. wind and solar). This process of storing a surplus to meet a future shortage is called PEAK SHAVING

• V2G systems • P2G systems • Heat energy • High volume storage • Molten salt • High thermal mass building materials • Kinetic energy • Electricity supercapacitors

the continuous reliable, affordable and sustainable availability of energy to meet the needs of society while minimising vulnerability to disruptions in supply